Since 1961, John has focused his practice on defense litigation in the following areas: health care provider liability, medical malpractice, product liability, professional liability, defamation, auto liability, premises liability, general liability and aviation liability. He joined Marshall Dennehey Warner Coleman & Goggin as a shareholder on July 1, 1996, and is a member of the Health Care Department.

John graduated from Princeton University in 1957 with a Bachelor of Arts in Economics and Sociology. He also attended the University of Pennsylvania Law School in Philadelphia, where he received his Bachelor of Laws degree in 1960. After completing active duty with the Pennsylvania Army National Guard, John joined the Wilkes-Barre, Pennsylvania, firm of Bedford, Waller, Griffith, Darling & Mitchell. He completed the remainder of his military tour with the U.S. Air Force Reserves.

In 1975, John formed the litigation firm of Griffith, Aponick & Musto, P.C., which in 1989 merged with the Wilkes-Barre firm Rosenn, Jenkins & Greenwald.

John is past president of the Pennsylvania Defense Institute and served on its board for many years prior to and following his term as president. He is also a fellow of the American College of Trial Lawyers and a diplomate of the American Board of Trial Advocates. John has been a guest lecturer at the Dickinson School of Law and has lectured at many seminars sponsored by the Pennsylvania Defense Institute and the Pennsylvania Bar Institute. He has been named a Pennsylvania Super Lawyer every year since 2004 in the area of personal injury defense.